Performance Standards

There are some recognized fenestration standards which are always evolving due to changes in manufacturing technology, building codes and rating system performance requirements. The most widely recognized and relevant standard is the North American Fenestration Standard (NAFS) which governs windows, doors, and skylights. Prepared as a joint collaboration between different organizations, the standard is known as AAMA/WDMA/CSA 101/I.S.2/A440. While this standard is familiar to many specifiers and fenestration manufacturers, the latest version referenced in the current International Building Codes has realigned and changed a bit. Most significantly, a not-so-recent change reduced the total number of Performance Class designations as defined by the Performance Grade (a set of performance requirements corresponding to a Design Pressure range) at the intended location of the building. It is important that specifiers recognize this change and not rely on older versions of this standard which included five performance classes, described as: “R” for Residential, “LC” for Light Commercial, “C” for Commercial, “HC” for Heavy Commercial and “AW” for Architectural. In the most current edition of NAFS, the “C” and “HC” performance classifications have been eliminated and a new “CW” classification has been added for Commercial fenestration. This reduces the total number of performance classifications from five to four and puts the emphasis for testing and performance on meeting the criteria for these Performance Grades.

To be classified into one of these four Performance Grade categories, independent testing is required based on the design pressure of wind forces acting on the fenestration (measured in pounds per square foot—psf) at a stated pressure difference (measured in pascals Pa). The entry-level or “gateway” criteria for tested fenestration units in each of the Performance Grades is as follows:

• R Class Fenestration: 15 psf (720 Pa) This class is commonly used in one- and two-family dwellings.
• LC Class Fenestration: 25 psf (1200 Pa) This class is the minimum designation appropriate for low- and mid-rise multifamily dwellings and other buildings where larger sizes and higher loading requirements are expected.
• CW Class Fenestration: 30 psf (1,440 Pa) This newest class is better suited to low- and mid-rise buildings where larger sizes, higher loading requirements, limits on deflection, and heavier use are expected.
• AW Class Fenestration: 40 psf (1,920 Pa) This is geared toward mid- and high-rise buildings to meet increased loading requirements and limits on deflection in buildings where frequent and extreme use of the fenestration products is expected.

These descriptions and testing levels are intended to act as a general guide in helping to determine which class is best suited for a particular application. In the case of multifamily buildings, it is clear that LC is the minimum classification needed. However, it is preferable, in most cases, to specify CW class fenestration for low- and mid-rise multifamily buildings to allow optimal performance in a greater range of design conditions.

In the case of large-format glass doors, both sliding and bi-folding versions, CW class units are now available from select manufacturers. That means that they have been independently tested and shown to meet the criteria to qualify for this preferred class of fenestration. This helps design professionals when selecting and specifying such products, but ultimately it means it benefits the owners and occupants of multifamily buildings. The ratings reflect performance features that help achieve the goal of reducing energy use while still meeting design intents. This adds to a building’s overall sustainability and visual appeal.

Conclusion

Creating efficient multifamily housing is a multifaceted task. The Passive House standard is one means to improve the energy efficiency while addressing cost-effective construction techniques. The building envelope can be enhanced with the proper use of WRBs, enhanced with drainable capability, and the cladding finished with aluminum trim. Cooling and heating can be provided with appropriately sized, high efficiency, VRF systems and air-source heat pumps. Fenestration can be addressed by selecting large-scale sliding or folding glass doors that provide light and ventilation along with high performance. These and other similar strategies lead to an overall design that meets the needs of the building owner, the occupants, and the environment.

BEST PRACTICES CASE STUDY

Photo courtesy of Tamlyn

Large-format bi-folding glass doors allow for full views and ventilation when open, and weather sealing and thermal performance when closed.

Study Type: Installation Best Practices for Drainable Building Wrap

The Issue: Sometimes a great product doesn’t perform as it should because it isn’t installed in the building properly.

The Solution: Following best practices as determined by product manufacturers or building science specialists can help assure that the intended performance is achieved. Architects or envelope commissioning agents making on-site inspections should be aware of the following best practice recommendations when drainable building wrap is installed.

Installation Process: Drainable building wrap should always be lapped in shingle fashion starting from the lowest point. This means that it is installed first from the bottom of the wall and the installers work their way up the wall. In this way, the required proper shingling of wrap layers allows the installed system to shed water to prevent water from entering the wall system. Further, when using drainable wrap as the primary air barrier, tape all seams using seam tape, always ensuring that the seam area is dry and clean. It is recommended that for best adhesion a hard roller or hand applicator is used.

With the above in mind, these are the typical, preferred installation steps:

• Unroll the drainable wrap with the spacers facing to the exterior.
• Drainable wrap should be installed shingle lap fashion (i.e. begin installation at the base of the wall assembly).
• Extend the drainable wrap a minimum of 2 inches over the sill plate.
• Fasten the first course of drainable wrap to the sheathing using cap fasteners.
• Seam tape is applied to the first course by removing one side of the release paper and, for best results, is laid down using a hard roller or hand applicator.
• With the first course in-place unroll the next course of drainable wrap maintaining the required overlaps with fastening stopping 9 inches from the bottom of this course allowing for it to be folded up.
• Overlap all horizontal seams by at least 6 inches, all vertical seams by at least 6 inches and corners by 12 inches.
• Fold the upper layer of the drainable wrap up and remove the release paper on the seam tape, then press the layers together using a hard roller or hand applicator. Then complete fastening along the seam.
• Continue the process above until the entire wall is properly covered.

There are also some general installation best practices to be aware of:

• Use only commonly available scissors to cut drainable wrap since the use of a utility knife will break the bond of the filaments (spacers).
• Fasteners should provide a minimum ¹⁄₂-inch penetration into the nail base and be spaced approximately 12 to 18 inches apart along the horizontal and vertical laps through seam tape. Fasten every 3 square feet everywhere else.
• Assure that the drainable wrap installation and flashing provide for positive drainage to the exterior of the assembly.
• Do not allow the drainable wrap to be exposed to sunlight in excess of 120 days. In fact, it is recommended that it be covered within 30 days.

The above practices apply to the solid wall areas where drainable wrap is being used. For windows, doors, and other openings, consult manufacturer recommended procedures for sealing and flashing around all of these building components.